An epoxy resin is cured by curing with various curing agents to form a cured body being generally excellent in the mechanical properties, water resistance, chemical resistance, heat resistance, electrical properties and the like, so that it is utilized in a wide range of fields such as adhesives, paints, laminated sheets, molding materials, casting materials, resists and so on. Lately, in the field of semiconductor-related materials are particularly overflowed electronic devices such as camera mobile-phones, super-thin liquid crystal and plasma TVs, lightweight notebook computers and so on using the term of light, thin, short, small or the like as a keyword, and hence very high characteristics are required even in packaging materials typified by the epoxy resin. Especially, leading-edge packages become complicated in their structures, and hence it is increasing a case that the sealing is difficult without a liquid sealant. For example, a package of a cavity-down type structure such as an enhanced BGA is necessary to be partially sealed, and therefore it cannot be prepared by a transfer molding. Because of this, it is demanded to develop a liquid epoxy resin having a high functionality.
Recently, RTM system is used as a composite material or a structural material for a vehicle body or a ship because of a simplicity of its production method. As a composition used in such materials is desired a low viscosity epoxy resin because of easy impregnation into carbon fiber or the like.
Heretofore, a compound obtained by reacting bisphenol A with epihalohydrin is known as an industrially most used liquid epoxy resin. However, it is pointed out that although such a bisphenol A-type epoxy resin is balanced physically, a cured material thereof is insufficient in the heat resistance, mechanical strength, humidity resistance and so on.
As a countermeasure to such problems, JP-A-2004-269705 and JP-A-2004-35702 report, for example, a way of adding and mixing a bisphenol F-type epoxy resin with a phenol aralkyl-type epoxy resin. By such a way are improved physical characteristics such as impact resistance and the like, but the resulting epoxy resin composition is still high in the viscosity. Therefore, it is desired to develop an epoxy resin having a lower viscosity and a high functionality.